Field of Technology
The present disclosure relates to methods for heat treating powder metallurgy nickel-base alloy articles. The present disclosure also is directed to powder metallurgy nickel-base alloys produced by the method of the present disclosure, and to articles including such alloys.
Description of the Background of the Technology
Powder metallurgy nickel-base alloys are produced using powder metallurgical techniques such as, for example, consolidating and sintering metallurgical powders. Powder metallurgy nickel-base alloys contain nickel as the predominant element, along with concentrations of various alloying elements and impurities, and may be strengthened by the precipitation of gamma prime (γ′) or a related phase during heat treatment. Components and other articles produced from powder metallurgy nickel-base alloys, e.g., discs for gas turbine engines, typically undergo thermo-mechanical processing to form the shape of the articles, and are heat treated afterwards. For example, the articles are forged and isothermally solution heat treated at a temperature below the γ′ solvus (subsolvus), followed by quenching in suitable medium, e.g., air or oil. A solution heat treatment below the γ′ solvus can result in a fine grain microstructure. The solution heat treatment may be followed by a lower temperature aging heat treatment to relieve residual stresses that develop as a result of the quench and/or to produce a distribution of γ′ precipitates in a gamma (γ) matrix.
In conventional processes, forged powder metallurgy nickel-base alloy articles are placed in a furnace at a start temperature in the furnace that is within 30° C. of the solution heat treatment temperature. The furnace set point is then recovered so that the articles reach the solution heat treatment temperature as fast as possible for completing the required heat treatment. However, the likelihood of critical grain growth in the articles may be increased by this conventional method of heat treating. Thus, there has developed a need for improved methods that overcome the limitations of conventional processes that increase the likelihood of critical grain growth in powder metallurgy nickel-base alloy articles.